The invention encompasses a system for the filtration of media, in particular such media which have an abrasive nature, and which are subsequently to be treated in a membrane filter system.
Filtration systems have become known in a variety of different configurations. They are generally supposed to be able to handle large quantities of medium per unit time, while exhibiting precise separation ability, i.e. effect as complete as possible a separation between the raw material and the desired product. These two functions stand in direct conflict with each other. One can increase the throughput by increasing the size of the flow opening. This will, however, reduce the precision of the separation.
A further problem is that, irrespective of what type of filtration surface is used, sooner or later a filter cake will be deposited on the surface, which will reduce the throughput and over time change the operating characteristics of the system. A number of mechanisms have been designed to prevent the formation of such a filter cake or layer, for example, the installation of scrapers which brush across the filtration surface to clear it of deposits. Agitation and turbulence inducing mechanism such as impellers are also employed to agitate the medium near the filtration surface.
The invention has the objectives of configuring a system of the type described above, which is able to handle large quantities of the medium to be filtered, while achieving a high degree of separation precision, and thereby removing all undesirable materials, in particular abrasive materials. The system also requires little space and has a lower energy consumption than conventional systems.
These objectives are achieved by the features of claim 1
By arranging the hollow discs of a pack of hollow discs in such a way that they mesh with the disc shaped structure of a neighboring pack, one can cause, by means of rotation of the two packs, the surfaces to run across each other. This leads to a cleaning of the surfaces and a reduction or prevention of deposition of solids.
A further benefit is derived from this design.
During the relative rotational motion of the packs, the radially external area of one disc will overlap the radially internal area of the other disc. If the discs of both packs rotate in the same direction the high rotational speed of one disc meets with the low rotational speed of the other disc so that the relative speed in the area of overlap between two plates is, therefore, essentially constant in the radial direction. This has a positive effect on the clearing action, which makes for optimum utilization of the sieve area, which in turn has a positive effect on the throughput
The term xe2x80x9cSievexe2x80x9d is understood to mean any type of sieve material. So, for example, a weave or felt can be used. Slotted or perforated sheet metal can also be considered. The size of the openings in the sieve is at least 5 xcexcm, but preferably larger than 20 xcexcm.
The invention comprises two main embodiments:
The first embodiment is to use a primary membrane pack, which comprises a hollow shaft as well as hollow discs the walls of which are constructed of a sieve material. A secondary pack comprises a shaft that need not be hollow, and with discs that can have either a sealed outer surface or are hollow.
If the discs of the secondary pack have sealed surfaces, then these discs achieve the one aim of causing agitation of the medium in the container, thereby avoiding the deposition of materials on the sieve surfaces of the primary pack.
If the discs of the secondary pack are also hollow, then the shaft of the secondary pack would also be hollow, allowing these hollow discs to be used to direct the medium to be treated, via suitable openings or nobles, against the surface of the filtering/sieving discs of the primary pack.
In the second embodiment of the invention, the secondary pack is constructed in the same manner as the primary pack. It has a hollow shaft, and hollow discs, the walls of which consist of sieve material.